Photodetector

Abstract

According to an embodiment, a photodetector includes a photodetecting element that has a pn junction and outputs a photocurrent corresponding to detected light, a voltage applying unit that applies a voltage to the photodetecting element, an obtaining unit that obtains the photocurrent detected by the photodetecting element, and a voltage controller. The voltage controller controls the voltage applying unit to apply, during a drive period, a drive voltage whose absolute value is not smaller than an avalanche breakdown voltage of the pn junction and which is in reverse bias with respect to the pn junction; and apply, during a standby period, any of a first standby voltage in forward bias, a second standby voltage with a voltage value of 0 V, and a third standby voltage whose absolute value is greater than 0 V, which is less than the drive voltage, and which is in reverse bias.

What is claimed is: 
     
       1. A photodetector comprising:
 a photodetecting element that has a pn junction and outputs a photocurrent corresponding to detected light; 
 a voltage applying unit that applies a voltage to the photodetecting element; 
 a first obtaining unit to obtain the photocurrent detected by the photodetecting element; and 
 a voltage controller to control the voltage applying unit to apply, during a drive period in which the photocurrent is obtained, a drive voltage and apply, during a standby period in which the photocurrent is not obtained, any of a first standby voltage, a second standby voltage with a voltage value of 0 V, and a third standby voltage, the drive voltage having a voltage value whose absolute value is equal to or greater than an avalanche breakdown voltage of the pn junction and being in reverse bias with respect to the pn junction, the first standby voltage being in forward bias with respect to the pn junction, and the third standby voltage having a voltage value whose absolute value is greater than 0 V and which is less than the drive voltage and being in reverse bias with respect to the pn junction. 
 
     
     
       2. The photodetector according to  claim 1 , comprising:
 a second obtaining unit to obtain a temperature of the photodetecting element during the drive period; and 
 a first calculator to calculate a voltage application condition for allowing the photodetecting element to generate Joule heat according to the temperature, wherein 
 the voltage controller controls the voltage applying unit to apply one of the first standby voltage, the second standby voltage, and the third standby voltage according to the voltage application condition. 
 
     
     
       3. The photodetector according to  claim 2 , further comprising a temperature detector to measure a temperature of the photodetecting element, wherein
 the second obtaining unit obtains a temperature of the photodetecting element during the drive period from the temperature detector. 
 
     
     
       4. The photodetector according to  claim 2 , further comprising a second calculator to calculate Joule heat generated in the photodetecting element during the drive period, based on time elapsed from a last transition from the standby period to the drive period and based on the drive voltage, wherein
 the first calculator calculates the voltage application condition for allowing the photodetecting element to generate Joule heat. 
 
     
     
       5. The photodetector according to  claim 1 , further comprising:
 a third obtaining unit to measure a current value flowing when the first standby voltage is applied; and 
 a third calculator to calculate a temperature of the photodetecting element based on the voltage value of the first standby voltage. 
 
     
     
       6. The photodetector according to  claim 1 , further comprising a scintillator provided on a light incident side of the photodetecting element and converting radiation into scintillation light.